02-14-2012 11:40 PM - edited 03-04-2019 03:16 PM
Hi,
I want vlan 124 use the second path (G2/1/4-G2/1/1), the other vlan use the first path (G1/1/4-G1/1/1)
Here is my conf for both switches :
SW1 :
spanning-tree mode rapid-pvst
spanning-tree extend system-id
spanning-tree vlan 8,62,120,125-126,128-129,172 priority 4096
spanning-tree vlan 124 priority 8192
interface GigabitEthernet1/1/4
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 8,62,120,124-126,128,129,172
switchport mode trunk
spanning-tree vlan 8,62,120,125-126,128-129,172 port-priority 64
SW2 :
spanning-tree mode rapid-pvst
spanning-tree extend system-id
spanning-tree vlan 8,62,120,125-126,128-129,172 priority 8192
spanning-tree vlan 124 priority 4096
interface GigabitEthernet2/1/1
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 8,62,120,124-126,128,129,172
switchport mode trunk
spanning-tree vlan 124 port-priority 64
Anyway, all trafic goes through G1/1/4-G1/1/1, even vlan 124....
SW1#sh spanning-tree vlan 124 det
VLAN0124 is executing the rstp compatible Spanning Tree protocol
Bridge Identifier has priority 8192, sysid 124, address 6400.f1a6.dc80
Configured hello time 2, max age 20, forward delay 15, transmit hold-count 6
Current root has priority 4220, address c464.130f.4180
Root port is 28 (GigabitEthernet1/1/4), cost of root path is 4
Topology change flag not set, detected flag not set
Number of topology changes 22 last change occurred 09:58:48 ago
from StackPort1
Times: hold 1, topology change 35, notification 2
hello 2, max age 20, forward delay 15
Timers: hello 0, topology change 0, notification 0, aging 300
Port 28 (GigabitEthernet1/1/4) of VLAN0124 is root forwarding
Port path cost 4, Port priority 128, Port Identifier 128.28.
Designated root has priority 4220, address c464.130f.4180
Designated bridge has priority 4220, address c464.130f.4180
Designated port id is 128.25, designated path cost 0
Timers: message age 16, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 8, received 17840
Port 84 (GigabitEthernet2/1/4) of VLAN0124 is alternate blocking
Port path cost 4, Port priority 128, Port Identifier 128.84.
Designated root has priority 4220, address c464.130f.4180
Designated bridge has priority 4220, address c464.130f.4180
Designated port id is 64.81, designated path cost 0
Timers: message age 15, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 7, received 20228
SW2#sh spanning-tree vlan 124 det
VLAN0124 is executing the rstp compatible Spanning Tree protocol
Bridge Identifier has priority 4096, sysid 124, address c464.130f.4180
Configured hello time 2, max age 20, forward delay 15, transmit hold-count 6
We are the root of the spanning tree
Topology change flag not set, detected flag not set
Number of topology changes 17 last change occurred 09:58:37 ago
from GigabitEthernet1/1/1
Times: hold 1, topology change 35, notification 2
hello 2, max age 20, forward delay 15
Timers: hello 0, topology change 0, notification 0, aging 300
Port 25 (GigabitEthernet1/1/1) of VLAN0124 is designated forwarding
Port path cost 4, Port priority 128, Port Identifier 128.25.
Designated root has priority 4220, address c464.130f.4180
Designated bridge has priority 4220, address c464.130f.4180
Designated port id is 128.25, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 17835, received 3
Port 81 (GigabitEthernet2/1/1) of VLAN0124 is designated forwarding
Port path cost 4, Port priority 64, Port Identifier 64.81.
Designated root has priority 4220, address c464.130f.4180
Designated bridge has priority 4220, address c464.130f.4180
Designated port id is 64.81, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 20223, received 7
Why the path is not used for vlan 124 ??? Where is the mistake ?
Solved! Go to Solution.
02-15-2012 02:02 AM
Hi,
sorry, I don't understand, the spanning-tree vlan 124 priority 4096 on SW2 is not enough ?
All this command is gonna do is make SW2 the root bridge but it won't have any effect on load-balancing.
the decision for electing the root port on a non root bridge is lowest Root Path Cost and in case of a tie which is the case here then the switch will elect as root port the one receiving the lowest Bridge id which are equal here too so then it will lookt at lowest received port-priority then if there is a tie the switch will look at lowest advertised port identifier. so the root port will be G1/1/4 for all VLANs as on SW2 G1/1/1 has lowest port identifier.
So as toshi stated you have two choices here :
1) raise the cost of G1/1/4 for VLAN 124 on SW1
2) lower port-priority of g2/1/1 for VLAN 124 on SW2
Regards.
Alain
02-14-2012 11:55 PM
Hi,
You just configure "port priority" on upstream switches on designated ports or modify "port cost" on downstream switches on root ports.
HTH,
Toshi
02-15-2012 12:31 AM
Hi,
sorry, I don't understand, the spanning-tree vlan 124 priority 4096 on SW2 is not enough ?
Pascal
02-15-2012 02:02 AM
Hi,
sorry, I don't understand, the spanning-tree vlan 124 priority 4096 on SW2 is not enough ?
All this command is gonna do is make SW2 the root bridge but it won't have any effect on load-balancing.
the decision for electing the root port on a non root bridge is lowest Root Path Cost and in case of a tie which is the case here then the switch will elect as root port the one receiving the lowest Bridge id which are equal here too so then it will lookt at lowest received port-priority then if there is a tie the switch will look at lowest advertised port identifier. so the root port will be G1/1/4 for all VLANs as on SW2 G1/1/1 has lowest port identifier.
So as toshi stated you have two choices here :
1) raise the cost of G1/1/4 for VLAN 124 on SW1
2) lower port-priority of g2/1/1 for VLAN 124 on SW2
Regards.
Alain
02-15-2012 03:40 AM
I have already a lower port-priority on G2/1/1, as you can see in my config.... but it doesn't work
spanning-tree vlan 124 port-priority 64
Look at the show spanning tree vlan detail on SW1 :
Port 28 (GigabitEthernet1/1/4) of VLAN0124 is root forwarding
Port path cost 4, Port priority 128, Port Identifier 128.28.
Designated root has priority 4220, address c464.130f.4180
Designated bridge has priority 4220, address c464.130f.4180
Designated port id is 128.25, designated path cost 0
Timers: message age 16, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 8, received 17840
Port 84 (GigabitEthernet2/1/4) of VLAN0124 is alternate blocking
Port path cost 4, Port priority 128, Port Identifier 128.84.
Designated root has priority 4220, address c464.130f.4180
Designated bridge has priority 4220, address c464.130f.4180
Designated port id is 64.81, designated path cost 0
Timers: message age 15, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 7, received 20228
Designated port id is lower (64.81 < 128.21) but it is in the alternate blocking state...
02-15-2012 04:42 AM
Hi,
Yes indeed then it's weird. Can you try shutting the interfaces and then bring them back up.
Regards.
Alain
02-15-2012 05:15 AM
Not really possible because I'm in a production environement.
Anyway, I've removed the
spanning-tree vlan 8,62,120,125-126,128-129,172 port-priority 64 on G1/1/4 and
spanning-tree vlan 124 port-priority 64 on G2/1/1 and added
spanning-tree vlan 8,62,120,125-126,128-129,172 cost 2 on G1/1/1 of SW2 and
spanning-tree vlan 124 cost 2 on G2/1/4 of SW1 and then, it does the job...
I still don't understand why the port-priority is not working... but now, with cost command, it works.
Thank you
02-15-2012 05:23 AM
Hi,
Happy you solved problem.
Don't forget to rate helpful posts and mark the thread as solved.
Regards.
Alain
02-15-2012 01:34 AM
I don't see the config for G2/1/4 on Sw1. I think you need to add the vlan 124 priority on that port and allow it.
Hope this helps
Eugen
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